Mass concentrations of PM1, PM2.5 and PM10 in air were measured at four EMEP stations in the Nordic countries during 2006. All stations used the same low-cost equipment for sampling PM1, but used different techniques for the other size fractions. The PM1 filters were analysed for inorganic ions for the first half of June. PM1 constituted on average more than half of the PM2.5 concentrations, but was on average less than half of the PM10 concentrations. There were two episodes of high PM1 concentrations during the year, one in May-June and another one in August-September. The highest PM1 concentrations were found during South-Easterly wind trajectories and lowest concentrations during northerly trajectories. Even though the annual average mass relations between the three size fractions were rather independent of the trajectory sectors, the fine and the coarse particle masses were not correlated on a daily basis. The PM2.5 concentration, which is the parameter that should be measured within EU, correlated fairly well with the concentration of accumulation mode particles (PM1). In June only a minor fraction of PM1 consisted of inorganic ions. Only ammonium and sulphate ions of the measured ions in PM1 were well correlated with one another.